Growing rhubarb
Officers of Department of Primary Industries and Fisheries, Queensland
Rhubarb (Rheum rhabarbarum) is an herbaceous perennial of the botanical family Polygonaceae. The succulent stems are used in sauces and pies, and can be eaten raw or stewed in desserts. The leaves contain oxalic acid and should not be eaten. Rhubarb production is labour-intensive during periods of weed control and harvesting.
Climate and soils
Rhubarb does best in cool climates but grows reasonably well in Queensland's sub-tropical environments, except under extremes of heat. Temperatures above 25oC will slow growth, suppress reddening of the stalks and may cause problems in plant establishment. The best stem colour is produced at about 10oC. Temperatures below -3oC will damage above ground plant parts.
Rhubarb can be grown on a wide range of soil types, providing they are well drained, but prefers deep loams well supplied with organic matter. The most satisfactory soil reaction range for rhubarb culture appears to be between pH 5.6 and pH 6.5 (moderate to slight acidity).
Propagation and planting
Rhubarb is usually propagated by planting pieces or divisions of 'crowns' formed during preceding seasons. Divisions are made by cutting down through the crown between the buds or 'eyes' leaving a piece of storage root material with each separate bud. Only disease-free crowns should be selected for division. High quality crowns are often difficult to obtain as established growers have selected quality types over a number of years, which suit the environment and market supplied.
Usually, rhubarb crowns should be divided after about 3 to 4 years of production, but division can be made earlier if the crown is becoming crowded with small buds which tend to produce small inferior stalks. Under ideal conditions, a strong, healthy division will produce a sturdy plant in one season's growth and some stems may be harvested in this first season. The outer buds on the older crowns are the most vigorous. Division and replanting is generally carried out in the spring and some small harvests can occur in early winter.
Crown divisions are usually set out at 90x90 cm or 90x120 cm spacings, covered with 5 to 7.5 cm of soil and firmly pressed into place. At these spacings, between 10 000 and 11 800 pieces are required per hectare.
Propagation using seed requires selection and culling over one or two seasons. Transplants are established at higher densities than when using crowns to allow for culling of poor types. Plants are selected for vigorous growth and stalk shape, thickness, length, tenderness and colour. Deep rich red stalks, over 30cm in length contribute to the highest yields and best returns.
Nutrition
Rhubarb has a high nutrient requirement and wherever possible large amounts of organic matter (at least 30 tonnes of animal manure per hectare) should be used. Manure mulches applied during the late autumn period can be worked carefully into the soil around the crowns. Additional fertiliser requirement will vary according to soil type. In the absence of a soil test and where animal manures are applied, side-dress using 400kg/ha of a 5:7:4 NPK or similar fertiliser mixture at three-monthly intervals when plants are actively growing or following each harvest.
Irrigation is essential if production of high-quality stalks is to be maintained. Rhubarb has a high water requirement, and any stress will affect stalk quality. Any check in growth will result in poor quality thin or pinched stalks.
After harvest, the plants are allowed to grow without hindrance, apart from removal of seed stalks. As soon as they appear, the seed stalks should be removed in order to conserve the crown's food reserves for the production of foliage and roots. A heavy crop of rhubarb in any year is a result of good crown vigour and heavy leaf development in the previous growing season. Continuity of supply to the market can be maintained by establishing several blocks which are consecutively harvested.
Pests and diseases
Weeds
Regular shallow cultivation is all that is usually required to control weeds, but some hand weeding may be necessary. No herbicides are registered in Queensland for weed control.
Insects
There are relatively few insect pests of rhubarb. Broad mites cause a bronzing effect on young leaves, inducing slow and weak growth. Stem borer enters the tip of the stem and burrows downwards leading to stem collapse. Snails may cause occasional damage.
Diseases
The most serious disease of rhubarb in Queensland is crown rot, caused by the fungus Phytophthora nicotianae var parasitica. The crown, roots and stem are affected by a rot which causes the whole plant to eventually collapse. It is important to ensure that internal and surface soil drainage is adequate. A registered fungicide dip can be used to treat crowns after division and prior to planting. Diseased crowns should not be used for propagation.
A number of other diseases of minor importance may also occur. Of these, downy mildew, rust and leaf spot are the most common.
Downy mildew, caused by the fungus Peronospora jaapiana, may occur during very wet weather where a downy growth may be visible on the undersurfaces of affected leaves. Large, light-brown spots up to 3 cm across develop, these drying out later to a papery texture. Affected plants should be heavily harvested and sprayed with a registered fungicide.
Rust (Puccinia rhei-undulate) is recognised by the small, raised rust-coloured pustules on the leaves and stalks. No fungicides are registered in Queensland for the control of this disease.
Leaf spot (Ascochyta rhei) is characterised by more or less circular, light-tan spots on leaves and sometimes on stems. Small black dots develop within these spots. No fungicides are registered in Queensland for the control of this disease.
Root knot and cyst nematodes have been recorded on rhubarb in Queensland but are not considered to be serious problems.
Harvesting and marketing
Harvesting of established crops occurs about every 6 to 8 weeks when 4 to 8 mature stalks can be harvested from each plant. The leaf stalks separate easily from the crown and are removed by grasping them near the base and pulling slightly to one side. Cool soon after harvest to prevent loss of quality of the stems. Leaves are removed or partly removed by trimming neatly to the end of the stem and the stalks tied in bundles which are graded for length, girth and colour. Rhubarb may also be pre-packaged under clear plastic wrap on polystyrene trays.
The size (weight or stalk number) of bunches and the packaging method will be determined by the market to be supplied. Check with the relevant agent, merchant or buyer for these specifications.
Yields are quite variable in Queensland, because of variable and unpredictable weather conditions and range from 0.5 to 1.5 kg/plant/year.
Further information
Current national information on agricultural chemicals registered for use on rhubarb is available on the Infopest CD-ROM. Write to GPO Box 46, Brisbane, Qld. 4001, email infopest@dpi.qld.gov.au or phone (07) 3239 3967 for further information.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
File No: H0011
Last updated 9 July 2004
